Do not ever enter start dates or end dates for a task.

Change the units.
I suspect you don't understand the relationship between work, duration, and units. I recommend that you get a book or at least do some online studying. This is not PowerPoint; the interface cannot teach all you need to know.

You are supposed to set up the plan in advance of starting working the project. Then save a baseline, then start working the plan. The baseline is a record of what you predicted before the project started so you can compare it to what actually happened.